Grain‐Boundary‐Rich Triphasic Artificial Hybrid Interphase Toward Practical Magnesium Metal Anodes

Abstract Magnesium metal anodes have attracted widespread attention for their high volumetric capacity and natural abundance, but are precluded from practical applications by poor rate capability and limited lifespan due to sluggish ion‐transfer kinetics and uneven deposition behavior. Herein, for the first time a grain‐boundary‐rich triphasic artificial hybrid interphase, consisting of Sb metal, Mg₃Sb₂ alloy, and MgCl₂, is designed on Mg anode surface by a facile solution treatment method, enabling high‐rate and long‐cycle Mg plating/stripping behavior. The triphasic artificial hybrid interphase affords high magnesiophilicity and ionic conductivity to reduce the energy barriers for Mg²⁺ desolvation and deposition. Meanwhile, the abundant grain boundaries redistribute Mg²⁺ flux at the electrode‐electrolyte interface and guide uniform Mg deposition. Accordingly, the as‐designed Mg metal anode achieves ultralong cycling life of 350 h at a high current density of 5 mA cm⁻² and a large areal capacity of 5 mAh cm⁻², outperforming previously reported Mg metal anodes with artificial interphases. Full cells with Mo₆ cathode also show extraordinary stability over a long lifespan of 8000 cycles at a high rate of 5 C. The rational artificial interphase design and the understanding of composition‐structure‐function relationships shed deep insights into the development of fast‐charging and long‐cycling Mg metal batteries.